Optimizing seawater temperature conditions to increase the productivity of ex situ coral nurseries

Large scale ex situ propagation of coral colonies for reef restoration is a relatively new and developing field. One of the many advantages of utilizing ex situ coral nurseries is the ability to optimize water quality conditions for coral health and survival. Slight alterations in environmental parameters (light, pH, temperature etc.) can affect the health and grow-out time of cultured coral, ultimately influencing production rates. However, corals are also subjected to pests associated with culture facilities such as ciliates, cyanobacterial blooms, and infectious diseases. Therefore, adjusting environmental parameters to optimize coral growth for a shorter ex situ residency time will lead to greater survival and faster restoration. Studies indicate that some coral species demonstrate parabolic tissue growth in response to increasing sea-surface temperatures until the maximum temperature tolerance is reached, whereafter they bleach. To maximize coral growth in Mote Marine Laboratory’s ex situ system, we tested the effect of two water temperature treatments (high temperature: 29.5 ± 0.03 °C; control: 25.2 ± 0.08 °C) on two coral species commonly used in reef restoration. To quantify this, we used four replicates of three genotypes each of Montastraea cavernosa (n = 12) and Acropora palmata (n = 12). Two-dimensional tissue area was recorded monthly using ImageJ and survival rates within each treatment were documented for 7 months. Results found that M. cavernosa had greater growth rates and equal survivorship in the high temperature treatment compared to the control treatment. A. palmata grew faster and had equal survivorship in the control treatment compared with the high temperature treatment. These results suggest that temperature preferences exist among coral species within ex situ systems and restoration practitioners should consider species-specific temperature regimes to maximize ex situ coral growth rates. This information is critical for optimizing production when corals are in the grow-out stage and should also be considered when designing ex situ systems to ensure temperature regulation can be controlled on a species-specific basis.